Paste for solar cell electrodes and solar cell manufactured using the paste

Abstract

The present invention relates to a conductive paste for solar cell electrodes comprising metal powder, glass frit, and an organic vehicle. Specifically, the conductive paste for solar cell electrodes, wherein the discharge rate factor A of a bus-bar electrode can be calculated using the following formula 1, and the discharge rate factor B of a finger electrode can be calculated using the following formula 2, can be calculated. A conductive paste for solar cell electrodes having a ratio of |A-B| of 0.100 or less can reduce manufacturing costs by reducing the discharge rate of the conductive paste. [Formula 1] A = (slip velocity × 10) / (G' × 0.01) [Formula 2] B = 1 / (G" × 0.01).

Description

Technical Field

[0001] The present invention relates to a conductive paste for forming an electrode of a solar cell and a solar cell manufactured using the conductive paste. Background Art

[0002] Conductive paste is a type of paste that has coating adaptability and is conductive after drying or firing. It is a fluid composition in which a conductive filler (metal filler) is dispersed alone or with glass frit in a carrier composed of a resin adhesive and a solvent. It is widely used in the formation of circuits and the external electrodes of ceramic capacitors.

[0003] Silver paste, in particular, has the highest chemical stability and the best conductivity among composite conductive pastes, making it widely used in a variety of fields, including conductive bonding, coating, and the formation of fine circuits. In electronic components such as printed circuit boards (PCBs), where reliability is paramount, silver paste is used for various purposes, such as silver through holes (STHs), adhesives, and coatings. It is also used as internal electrodes in multilayer capacitors and, more recently, as an electrode material in silicon solar cells.

[0004] However, conductive paste containing silver accounts for a significant portion of the price of solar cell materials. Therefore, as a result of research efforts to reduce the lay-down of front electrode paste in order to lower costs, methods have been developed to reduce the amount of silver paste remaining in the mask.

[0005] However, the technology for reducing the discharge amount of conductive paste does not take into account the variables caused by the area difference between the bus-bar electrode and the finger (filger) electrode. Therefore, it may cause the problem of excessive discharge amount in the bus-bar electrode, or when the discharge amount is reduced, the reduction in the discharge amount of the finger electrode may cause a large number of short circuits and lead to a decrease in the efficiency of the solar cell. Summary of the Invention

[0006] An object of the present invention is to provide a conductive paste that can reduce costs and maintain or improve efficiency by adjusting the discharge rate when printing on electrodes.

[0007] Another object of the present invention is to provide a conductive paste that can provide efficiency equal to or greater than that of reducing the discharge amount by developing factors related to the discharge amount of the slurry from busbar electrodes and factors related to the discharge amount of the slurry from finger electrodes and satisfying the conditions of each factor.

[0008] However, the purpose of the present invention is not limited to the purpose mentioned in the above content, and relevant practitioners will be able to further clearly understand other purposes not mentioned through the following description.

[0009] The present invention provides a conductive paste characterized by comprising metal powder, glass frit, and an organic vehicle. The discharge rate factor A of a bus-bar electrode can be calculated by the following formula 1, and the discharge rate factor B of a finger electrode can be calculated by the following formula 2, wherein |AB| is less than 0.100.

[0010] [Formula 1]

[0011] A=(Slip velocity×10) / (G'×0.01)

[0012] [Formula 2]

[0013] B = 1 / (G" × 0.01)

[0014] (G' is the elasticity value at 1% shear strain, and G" is the elasticity value at 90% shear strain)

[0015] Furthermore, the present invention is characterized in that the |AB| is 0.050 or less.

[0016] Furthermore, the present invention is characterized in that the A is 0.200 to 0.350, and the B is 0.200 to 0.230.

[0017] Furthermore, the present invention is characterized in that the conductive paste contains an ethyl cellulose-based resin, and the weight of the resin relative to 100 weight % of the conductive paste is 0.12 to 0.3 weight %.

[0018] Furthermore, the present invention is characterized in that: the conductive paste contains silicone oil,

[0019] The silicone oil includes at least one selected from decamethyltetrasiloxane, dodecamethylpentasiloxane, tetradecamethylhexasiloxane, hexadecamethylheptasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, and tetradecamethylcycloheptasiloxane.

[0020] Furthermore, the present invention is characterized in that the weight of the silicone oil is 0.5 to 1.5 wt % relative to 100 wt % of the conductive paste.

[0021] The present invention provides a conductive paste capable of reducing production costs by adjusting the discharge amount of the paste when printing on an electrode.

[0022] Specifically, the present invention can provide a conductive paste with an efficiency equal to or greater than that of reducing the discharge amount by developing factors related to the discharge amount of the slurry for busbar electrodes and for finger electrodes and satisfying the conditions of each factor. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figures 1 to 6 FIG. 1 is a schematic diagram illustrating a storage modulus measurement chart of a conductive paste manufactured according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] Before describing the present invention in detail, it should be understood that the terms used in this specification are intended only to describe specific embodiments. The scope of the present invention is not limited by the terms used, but is defined solely by the appended claims. Unless otherwise specified, all technical and scientific terms used in this specification have the same meanings as those commonly understood by persons of ordinary skill in the art.

[0025] Unless otherwise stated, the terms comprise, comprise, and comprising used throughout this specification and claims mean that the object, step, or series of objects and steps mentioned are included, but do not exclude the possibility of the existence of any other object, step, or series of objects or steps.

[0026] Furthermore, unless otherwise expressly stated to the contrary, each embodiment of the present invention may be implemented in combination with other embodiments. In particular, a feature described as being preferred or advantageous may be combined with other features or features described as being preferred or advantageous. Next, embodiments of the present invention and related effects will be described with reference to the accompanying drawings.

[0027] In this specification, a conductive paste for forming a front electrode of a solar cell, particularly a paste comprising conductive metal powder, glass frit, and an organic vehicle, will be taken as an example for description.

[0028] The slurry applicable to the present invention can satisfy the factors related to the slurry discharge amount of the busbar electrode and the factor conditions related to the slurry protrusion amount of the finger electrode, thereby reducing unnecessary discharge amount of the busbar electrode while maintaining an appropriate level of slurry discharge amount to prevent the finger electrode from breaking.

[0029] Specifically, the relative value of the discharge amount factor A of the busbar electrode using the slurry of the present invention is calculated by the following formula 1, and the relative value of the discharge amount factor B of the finger electrode is calculated by the following formula 2.

[0030] [Formula 1]

[0031] A=(Slip velocity×10) / (G'×0.01)

[0032] [Formula 2]

[0033] B = 1 / (G" × 0.01)

[0034] (G' is the elasticity value at 1% shear strain, and G" is the elasticity value at 90% shear strain)

[0035] A shear strain of 1% refers to the deformation rate of the slurry on the larger opening, i.e., the busbar electrode, while a shear strain of 90% refers to the deformation rate of the slurry on the smaller opening, i.e., the finger electrode.

[0036] The paste can be manufactured so that |AB|, calculated using Equations 1 and 2, is less than 0.100. Preferably, |AB| is less than 0.050, and even more preferably, less than 0.010. Conductive paste manufactured to meet this range can reduce the amount of paste discharged on busbar electrodes while maintaining or increasing the amount of paste discharged on finger electrodes, thereby reducing the overall amount of paste discharged. Despite this, conversion efficiency can be maintained or improved when used as solar cell electrodes.

[0037] The conductive paste to which the present invention is applied contains an organic vehicle, and by changing the content of the organic binder contained in the organic vehicle, a conductive paste with a reduced discharge amount during printing can be produced.

[0038] The type of organic binder is not particularly limited. Examples of cellulose ester compounds include cellulose acetate and cellulose acetate butyrate; examples of cellulose ether compounds include ethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl methyl cellulose; examples of acrylic compounds include polyacrylamide, polymethacrylate, polymethyl methacrylate, and polyethyl methacrylate; and examples of vinyl compounds include polyvinyl butyral, polyvinyl acetate, and polyvinyl alcohol. At least one organic binder can be used, preferably ethyl cellulose resin.

[0039] Furthermore, the conductive paste may contain 0.12 to 0.3 wt % of the organic binder based on 100 wt % of the conductive paste. Specifically, the conductive paste may contain 0.13 to 0.2 wt % based on 100 wt % of the conductive paste.

[0040] Furthermore, the paste to which the present invention is applied contains silicone oil, and by changing the content of the silicone oil, a conductive paste with a reduced discharge amount during printing can be produced.

[0041] The type of the silicone oil is not particularly limited. Preferably, linear molecules, branched molecules, cyclic molecules or a mixture thereof are used.

[0042] Specifically, the silicone oil as a linear molecule can be exemplified by decamethyltetrasiloxane, dodecamethylpentasiloxane, tetradecamethylhexasiloxane, and hexadecamethylheptasiloxane, while as a cyclic molecule, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, and tetradecamethylcycloheptasiloxane can be exemplified. The silicone oil can be selected to use at least one. In addition, the silicone oil can include one or more selected from the group consisting of phenyl trimethicone, dimethicone, cyclomethicone, polydimethylsiloxane, and silicone gum, and modified silicone oil can also be used. Preferably, polysiloxane such as polydimethylsiloxane can be used. In consideration of slip properties, unmodified polysiloxane oil is preferably used.

[0043] In addition, the molecular weight of the silicone oil is preferably 1 to 100,000 cs. If the molecular weight of the silicone oil exceeds 100,000 cs, the viscosity may be too high, making it difficult to prepare the slurry.

[0044] The silicone oil is included in an amount of 0.1 to 5% by weight, based on the total weight of the conductive paste composition. If the silicone oil is added at less than 0.1% by weight, the improvement in slip properties may be minimal. If the silicone oil is added at more than 5% by weight, phase separation and storage stability issues may occur. Furthermore, if the slip properties are too high, poor coating during printing may cause short circuits. Preferably, the silicone oil is included in an amount of 0.5 to 1.5% by weight.

[0045] Next, the conductive paste with reduced discharge volume to which the present invention is applied will be described in detail with reference to specific examples.

[0046] Specifically, the calculated discharge rate factor A of the busbar electrode and the calculated discharge rate factor B of the finger electrode are used to illustrate the conductive paste that can be expected to reduce the discharge rate. The discharge rate reduction effect of the paste applicable to the present invention is verified by comparing the expected discharge rate of the paste with the actually measured discharge rate of the paste and the power generation efficiency.

[0047] Test Example 1

[0048] (1) Test Example 1a

[0049] 85-95 g of silver powder, 1-4 g of glass frit, 6.02 g of a solvent as an organic vehicle, 0.1-0.4 g of a dispersant, 0.1-0.6 g of a surfactant, 0.1-1.2 g of an additive, 0.10 g of an ethyl cellulose resin, and 0.4-2.0 g of polydimethylsiloxane (PDMS) were mixed using a rotational stirring rotary device (Condition Mixer) and then dispersed using a three-roll mill to obtain a conductive paste (100 g).

[0050] (2) Test Example 1b

[0051] The same amounts and methods as in Test Example 1a were used except that 6.0 g of the solvent and 0.12 g of the ethyl cellulose resin were added.

[0052] (3) Test Example 1c

[0053] The same amounts and methods as in Test Example 1a were used except that 5.98 g of the solvent and 0.14 g of the ethyl cellulose resin were added.

[0054] (4) Test Example 1d

[0055] The same amounts and methods as in Test Example 1a were used except that 5.96 g of the solvent and 0.16 g of the ethyl cellulose resin were added.

[0056] Measurement of G', G" and slip velocity

[0057] The G' and G" values under different shear strains were measured using a five-interval thixotropy test (5ITT), with the shear strain set to five different intervals. Specifically, the 5ITT was conducted using Anton Paar MCR302 and PP50 / P3 at 25±1°C with a measuring gap of 1.2mm. Furthermore, the slip velocity was measured using Anton Paar MCR302 and PP50 / P3 at 25±1°C with a measuring gap of 0.6mm and a shear stress of 0 to 800Pa.

[0058] The shear strain values for each zone in the five-zone thixotropy test (5ITT) are as follows. Zone (II) shows the elasticity value G' at 1% shear strain, indicating the slurry deformation rate on the busbar electrode. Zone (IV) shows the elasticity value G" at 90% shear strain, indicating the slurry deformation rate on the finger electrodes. Zones (I), (III), and (V) show the elasticity values at 0.01% shear strain, which are included to ensure the accuracy of the elasticity values for (II) and (IV).

[0059] Figure 1 This is a graph showing the elasticity value based on the ethyl cellulose resin content. Figure 2 This is a graph showing the slip velocity according to the ethyl cellulose resin content.

[0060] like Figure 1 As shown in FIG, it can be confirmed that when the content of ethyl cellulose resin increases, the elasticity in the (II) range becomes higher, while the elasticity can be stably maintained in other ranges. Figure 2 As shown, it was confirmed that the slip velocity can be maintained substantially stably regardless of the content of the ethyl cellulose resin.

[0061] Figure 1 as well as Figure 2 The G′, G″ and slip velocity in , and the ejection rate factors A and B of the busbar electrode and the finger electrode calculated by the above formula 1 and formula 2 are shown in the following Table 1.

[0062]

Table 1

[0063]

[0064] like Figure 1 、 Figure 2 As shown in Table 1, as the ethyl cellulose resin content increases, G' increases and the busbar electrode discharge factor A decreases, while the slip velocity remains roughly the same. Therefore, it can be expected that the busbar electrode discharge area will decrease. Furthermore, since G" remains roughly the same, it can be expected that the finger electrode discharge area will remain the same.

[0065] In order to verify the predicted values, when Test Examples 1a to 1d were actually printed on a screen mask, the discharge amount, the measured areas of the busbar electrodes and finger electrodes, and the efficiency of the solar cell using the slurry as an electrode are shown in Table 2 below.

[0066]

Table 2

[0067]

[0068] As shown in Table 2, Figure 1 as well as Figure 2 As predicted, increasing the ethyl cellulose content actually reduces the busbar electrode area while maintaining the same finger electrode area, confirming a decrease in overall slurry discharge. Conversely, the solar cell efficiencies of Test Examples 1b to 1d, which have higher ethyl cellulose resin contents, improved compared to Test Example 1a.

[0069] Test Example 2

[0070] (1) Test Example 2a

[0071] 85-95 g of silver powder, 1-4 g of glass frit, 6.2 g of a solvent as an organic vehicle, 0.1-0.4 g of a dispersant, 0.1-0.6 g of a surfactant, 0.1-1.2 g of an additive, 0.1-0.4 g of an ethyl cellulose resin, and 0.6 g of polydimethylsiloxane (PDMS) were mixed using a rotational stirring rotary device (Condition Mixer) and then dispersed using a three-roll mill to obtain a conductive paste (100 g).

[0072] (2) Test Example 2b

[0073] The same amounts and methods as in Test Example 2a were used except that 6.0 g of the solvent and 1.0 g of polydimethylsiloxane (PDMS) were added.

[0074] (3) Test Example 2b

[0075] The same amounts and methods as in Test Example 2a were used except that 5.8 g of solvent and 1.4 g of polydimethylsiloxane (PDMS) were added.

[0076] (4) Test Example 2c

[0077] The same amounts and methods as in Test Example 2a were used except that 5.6 g of solvent and 1.8 g of polydimethylsiloxane (PDMS) were added.

[0078] Measurement of G', G" and slip velocity

[0079] Similar to Test Example 1, the G' and G" values under different shear strains were measured using a five-interval thixotropy test (5ITT), with the shear strain set to a total of five different intervals. Specifically, the 5ITT measurement conditions and measurement tools were Anton Paar MCR302 and PP50 / P3 at 25±1°C, with a measurement gap of 1.2 mm. Furthermore, the slip velocity measurement conditions and measurement tools were Anton Paar MCR302 and PP50 / P3 at 25±1°C, with a measurement gap of 0.6 mm, and the shear stress was measured in the range of 0 to 800 Pa.

[0080] The shear strain values for each zone in the five-zone thixotropy test (5ITT) are as follows. Zone (II) shows the elasticity value G' at 1% shear strain, indicating the slurry deformation rate on the busbar electrode. Zone (IV) shows the elasticity value G" at 90% shear strain, indicating the slurry deformation rate on the finger electrodes. Zones (I), (III), and (V) show the elasticity values at 0.01% shear strain, which are included to ensure the accuracy of the elasticity values for (II) and (IV).

[0081] Figure 3 This is a graph showing the elasticity value based on the polydimethylsiloxane (PDMS) content. Figure 4 This is a graph illustrating the slip velocity according to the polydimethylsiloxane (PDMS) content.

[0082] like Figure 3 As shown in FIG. 1 , it can be confirmed that when the content of polydimethylsiloxane (PDMS) increases, the elasticity G' of the (II) interval decreases slightly or remains the same, while the elasticity G" of the (IV) interval increases slightly or remains the same. Figure 4 As shown in FIG, it can be confirmed that as the content of polydimethylsiloxane (PDMS) increases, the slip velocity also increases.

[0083] Figure 3 as well as Figure 4 The G′, G″ and slip velocity in , and the ejection rate factors A and B of the busbar electrode and the finger electrode calculated by the above formula 1 and formula 2 are shown in the following Table 3.

[0084]

Table 3

[0085]

[0086] like Figure 3 、 Figure 4 As shown in Table 3, as the PDMS content increases, G' remains roughly the same, while the slip velocity increases. Therefore, it is expected that the ejection area of the printed busbar electrode will increase. Furthermore, as the PDMS content increases, G" also increases, which suggests that the ejection area of the finger electrodes will decrease.

[0087] At the same time, when the polydimethylsiloxane (PDMS) content is too low, the busbar electrode's discharge factor A is low, so the busbar electrode's discharge area will be reduced, while the finger electrode's discharge factor B is high, so the protruding area of the finger electrode will increase. Therefore, it can be judged that its efficiency will be the highest. However, due to the reduction in the accumulation of the overall discharge volume and the significant reduction in slip velocity, it may lead to the occurrence of circuit breaker and a significant decrease in efficiency.

[0088] In order to verify the predicted values, when Test Examples 2a to 2d were actually printed on a screen mask, the discharge amount, the measured areas of the busbar electrodes and finger electrodes, and the efficiency of the solar cell using the slurry as an electrode are shown in Table 4 below.

[0089]

Table 4

[0090]

[0091] As shown in Table 4, in Test Examples 2a to 2d, Figure 3 as well as Figure 4As predicted in the experiment, in fact, with the increase of polydimethylsiloxane (PDMS) content, the area of the busbar electrode increases and the area of the finger electrode decreases or remains the same, which confirms that the overall slurry discharge volume increases. In addition, in Experiment 2b to Experiment 2d, the efficiency of the solar cell in Experiment 2d is reduced compared with Experiment 2b and Experiment 2c. In Experiment 2a, because the amount of polydimethylsiloxane (PDMS) is not enough to improve the slippage of the slurry during printing, its discharge volume is reduced, but the efficiency is reduced because more disconnections and short circuits occur.

[0092] The features, structures, and effects described in the various embodiments described above can be combined or modified with other embodiments by a person having general knowledge in the technical field of the present invention. Therefore, the contents related to the above combinations or modifications should also be interpreted as being included in the scope of the present invention.

Claims

1. A conductive paste, characterized in that: As a slurry containing metal powder, glass frit and organic vehicle, The discharge factor A of the busbar electrode can be calculated by the following formula 1: The discharge factor B of the finger electrode can be calculated by the following formula 2: │AB│ is less than 0.100, [Formula 1] A = (slip velocity × 10) / (G' × 0.01) [Formula 2] B = 1 / (G" × 0.01) Where G' is the elastic value at a shear strain of 1%, and G" is the elastic value at a shear strain of 90%.

2. The conductive paste according to claim 1, wherein: The |AB| is less than 0.

050.

3. The conductive paste according to claim 1, wherein: The A is 0.200 to 0.350, and the B is 0.200 to 0.

230.

4. The conductive paste according to claim 1, wherein: The conductive paste includes an ethyl cellulose-based resin, and the weight of the resin relative to 100 weight % of the conductive paste is 0.12 to 0.3 weight %.

5. The conductive paste according to claim 1, wherein: The conductive paste contains silicone oil, The silicone oil is selected from at least one of decamethyltetrasiloxane, dodecamethylpentasiloxane, tetradecamethylhexasiloxane, hexadecylheptasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane and tetradecamethylcycloheptasiloxane.

6. The conductive paste according to claim 5, wherein: The weight of the silicone oil is 0.5 to 1.5 weight % relative to 100 weight % of the conductive paste.

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